The present invention relates to a system for and a method of press-fitting parts such as bearings into other components or workpieces such as casings.
Various mechanical parts such as bearings, bushings, or the like are press-fitted into other components or workpieces such as casings. In many applications, a plurality of parts are press-fitted into a single casing, and there is a demand for the mass production of such casings with press-fitted parts. Manual procedures for press-fitting parts into casings are quite inefficient, and cannot be relied upon in mass production processes. Therefore, automatic apparatus for press-fitting parts into other workpieces have been desired and actually developed to meet the demand.
Various automatic press-fitting apparatus have been proposed. One technical achievement of such an automatic press-fitting arrangement is disclosed in Japanese Patent Publication No. 49-22744, for example. The disclosed apparatus includes a frame having a stationary reference surface, a pallet for supporting a casing, the pallet being movable toward and away from the frame, and a pair of presser rods for press-fitting a pair of bushings into the casing from its opposite ends, the presser rods being movable toward and away from each other.
In operation, a casing is first placed on the pallet, and then one of the presser rods is moved toward the casing and press-fits a bushing, held on the end of the presser rod, into a hole defined in the casing. The other presser rod is also moved to cause its shoulder to press the casing, thereby pushing the pallet toward the frame until the end face of the pallet is held against the stationary reference surface. Then, the other presser rod is displaced toward the casing to press-fit a bushing, held on this presser rod, into the casing.
After one of the bushings has been press-fitted into the casing by one of the presser rods, the pallet is held against the stationary reference surface. Therefore, the casing is not positioned directly by the stationary reference surface. If the casing is not properly positioned and the presser rod is not aligned with the hole in the casing, then the bushing may be skewed with respect to the casing and press-fitted into the casing by the presser rod.
Japanese Patent Publication No. 52-23112 discloses an automatic press-fitting apparatus capable of simultaneously press-fitting two parts into a workpiece. The disclosed apparatus has a pair of presser units mounted by joints on the piston rod extending from a single cylinder, the presser units holding respective parts through chucks. When the cylinder is actuated, the parts supported by the presser units are simultaneously press-fitted into the workpiece.
When the parts are press-fitted into the workpiece, it is necessary to exert relatively large forces on the parts. In view of this, the presser units are moved at a considerably low speed. The presser units are also moved at a low speed when they are displaced from a retracted position to a position where the parts start to be press-fitted by the presser units. Therefore, a relatively long period of time is required to move the presser units before and after the parts are press-fitted into the workpiece. Consequently, the entire process of press-fitting the parts cannot be performed efficiently.
Moreover, since the two parts are simultaneously press-fitted into the workpiece by the single cylinder, the cylinder is necessarily large in capacity and hence size because of the relatively large force needed to press-fit each of the parts into the workpiece. At the time the two parts are simultaneously press-fitted into the workpiece, the workpiece is subjected to an undue load, and tends to be elastically deformed or otherwise damaged.
While the parts are being press-fitted into the workpiece in response to the operation of the cylinder, the presser units undergo reactive forces from the parts being press-fitted. The greater the forces applied to press-fit the parts, the greater the reactive forces acting on the presser units. The reactive forces may be too large to properly and reliably press-fit the parts into the workpiece. If the cylinder is increased in its capacity for reliable operation, then it does not operate efficiently and the entire apparatus is increased in size.
In cases where the parts to be press-fitted are bushings or the like, they have oil holes for passage of oil. When these parts are press-fitted into a workpiece, the oil holes of the parts must be held in exact registry with corresponding oil holes defined in the workpiece. There have been proposed various devices for automatically phasing the parts with the workpiece. One of such automatic phasing machines is disclosed in Japanese Laid-Open Utility Model Publication No. 62-98621.
According to the disclosed arrangement, a part is positioned and held on a presser head by fingers which are spread by a spherical body engaging a resilient member. However the part tends to turn into a different angular position when the presser head is moved into a position where the part is to be press-fitted. At the time the part is press-fitted into a workpiece, the part is liable to turn due for example to the difference between local resistances to the press-fitting action. The part may be press-fitted into the workpiece while the oil hole in the part is being positioned out of registry with the oil hoe in the workpiece. Therefore, the efficiency of the process of press-fitting parts into workpieces remains low.
Japanese Laid-Open Patent Publication No. 60-228033 discloses a parts supply device for supplying different parts at spaced intervals to an automatic press-fitting apparatus of the type described above.
The disclosed parts supply device is positioned behind the automatic press-fitting apparatus. After parts have been fed to the presser rods of the automatic press-fitting apparatus, the automatic press-fitting apparatus is turned until the parts confront a workpiece. Then, the workpiece and the presser rods are displaced toward each other to press-fit the parts into the workpiece. The turning movement of the automatic press-fitting apparatus, however, makes the press-fitting procedure inefficient. If the parts supply device is employed in the mass production of components of one kind, parts cannot quickly be press-fitted into workpieces. Since the parts supply device is placed rearwardly of the automatic press-fitting apparatus and the automatic press-fitting apparatus is turned, the space which is required by the parts supply device and the automatic press-fitting apparatus is relatively large.